1. Field of the Invention
The present invention relates to a push-button switch employed for turning on and off of various kinds of electronic appliances such as audio instruments, and more particularly, to a push-button switch of an illumination type which controls turning-on and -off of a switching mechanism accommodated within a switch body while it is fixedly inserted into a mounting socket and which has an illumination lamp provided therewithin for indication of the switch.
2. Description of the Prior Art
A push-button switch of the type referred to above has conventionally been known to be provided with a plunger at one side in a housing and a switching mechanism at the other side in the housing. This push-button switch controls the turning-on and -off of the switching mechanism through an alternate cam and the plunger moving in association with the pressure application thereto.
Meanwhile, it has been general that the sliding portions of the alternate cam and the plunger described above are applied with grease for the purpose of improving the sliding action and the service life thereof.
However, it has been a problem that the grease applied to the sliding portions may percolate the part of the switching mechanism, resulting in an inferior connection between contact points or reduction of connection reliability.
Therefore, in order to solve the above-described problem, the alternate cam and the plunger described above have been generally made of fluorine compound resin. However, this kind of resin is limited in its usage and therefore small in production amount. Moreover, the material for the resin is expensive, and therefore, the push-button switch made of this resin becomes unfavorably high in the manufacturing cost thereof, and is disadvantageous because of shorter service life, in comparison with one applied with grease.
Further, there has conventionally been known such a push-button switch as referred to above that is provided with a switch mechanism having the construction as follows. That is, one end of an operating member of a generally W-shape is engaged at a corner of a fixed terminal in inverted L-shaped configuration, and at the same time, a tension spring is stretched between the fixed terminal and a movable member such that the spring force of the tension spring is added to the operating member through the movable member. The other end of the operating member is moved in association with the depression of the plunger. Accordingly, when the plunger is depressed, a contact point formed at the free end of the movable member is brought into pressed contact with another fixed terminal opposed to the contact point.
However, the above-described switch mechanism is so small that it should be assembled by hand with the help of a pincette. Moreover, since the movable member is inevitably biased by the spring force of the tension spring during the assembling of the switch mechanism, there is a possibility that the operating member and the movable member be separated away from each other by the spring force, if the switch mechanism is not skillfully assembled.
Additionally, the above described inverted L-shaped fixed terminal has only its bottom end portion supported by a base, without any support means for its upper end portion. Therefore, when the fixed terminal is biased by the spring force of the above tension spring, particularly during the assembling time of the switch mechanism and the life cycle, the upper end portion of the fixed terminal may possibly be slipped or displaced, resulting in the change of the spring load of the tension spring which will be a cause for an unstable switching operation.
Furthermore, the prior art push-button switch is provided with a switch mechanism wherein a tension spring is stretched between the fixed terminal and the movable member such that the operating member is biased through the movable member by the spring force of the tension spring, while the other end of the operating member is moved in association with the depression of the plunger such that a coil spring provided with the plunger is compressed at the depression of the plunger, thereby to displace the operating member so as to bring a contact point formed at the free end of the movable member into pressed contact with another fixed terminal opposed to the contact point. In the prior art push-button switch having the switch mechanism as described above, the returning position of the switch has been determined by the balance between the coil spring and the tension spring. However, it is disadvantageous that the returning position of the operating member may undesirably be changed each time or the returning action may be hampered due to the unevenness found in the spring load of the coil spring and the tension spring, and the reduction of the spring force.
In the meantime, it has been impossible that the push-button switch of this illumination type is used as an indication lamp because each component part has a different structure. On the other hand, in the case that an indication lamp is to be added to an apparatus equipped with the push-button switch, more space is required for the indication lamp only. Moreover, in this case, an erroneous switching operation may be given rise to. For preventing such an erroneous switching operation, a special component part therefor becomes necessary, thereby enlarging the size of the switch. It is also disadvantageous that the total number of component parts is increased thereby to raise the cost for management of the switch.